perf(decode): slim decode response to id + display summary

POST /vehicles/decode returned the full vehicles row while every consumer
(search, landing, service-test) only navigates by id and re-fetches via
GET /vehicles/:id. That shipped the raw upstream decode payload to the
client on every decode — rawData is 19KB avg / 127KB p95 / 207KB max in
prod — plus the provider name, for nothing.

The response is now { id, brandName, model, year } on both the DB-hit and
fresh-decode paths. Frontend drops the (now absent) source property from
the vin_decode_success event; decode source remains queryable server-side
via query_logs.source.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/web/src/routes/dashboard/search.tsx

@@ -299,7 +299,6 @@ function SearchPage() {
         vin: cleanVin,
         vehicle_id: data.id,
         response_time_ms: responseTimeMs,
-        source: data.source ?? null,
         query_source: querySourceRef.current,
       });
       navigate({ to: "/dashboard/vehicles/$id", params: { id: data.id } });